This proposal is in response to an NIH announcement for the Fogarty International Research Collaboration Award (FIRCA) in association with my MERIT Award 4R37 GM15591. Blood coagulation disorders are a worldwide medical problem. Among them, thrombosis, the occlusion of a blood vessel, is a leading killer throughout the world. Certain snakes, especially Crotalidae (pit vipers) and Viperidae (vipers), have a pronounced effect on blood coagulation. Some components prevent coagulation by hydrolyzing fibrinogen and/or fibrin. By using a chemical fractionation method, nontoxic anticoagulants can be separated from toxic fractions. Lebetase will be isolated from the venom of Vipera lebetina captured in the Uzbek region. In order to develop lebetase as a thrombolytic agent, many investigations related to safety, fibrinolytic effect in vivo, and the effect on platelet aggregation should be done. Thrombolysis will be tested on rats by artificially producing a thrombus and then examining the progress of recanalization after injecting lebetase. The LD50 will also be determined to ensure low toxicity. It is also proposed to determine the amino acid sequence of lebetase. By knowing the primary structure, the synthesis of lebetase either by peptide synthesis or by DNA cloning technique can be accomplished in the future. The proposed research may develop an effective treatment of thrombosis by directly dissolving the thrombus.